The present invention relates to a single stage, multilayered catalyst system for hydrodehazing and hydrofinishing a hydrocracked, solvent dewaxed lube oil base stock. In the first layer, the hydrocracked, solvent dewaxed stock is catalytically dehazed, using, for example, a high constraint index aluminosilicate zeolite catalyst. In the second layer, the catalytically dewaxed stock is hydrofinished using, for example, a palladium hydrotreating catalyst having an alumina or siliceous matrix.
This invention also relates to a process for hydrodehazing and hydrofinishing a hydrocracked, solvent dewaxed lube oil base stock. The process comprises contacting the base stock with hydrogen in the presence of the multilayered catalyst system. Specifically, I have found that by using high space velocity rates and a high hydrogen partial pressure, both hydrodehazing and hydrofinishing are accomplished in a single process step using the layered catalyst system with minimum yield, VI, and pour point loss.
It is well known in the art to form various lubricating oils from hydrocarbon fractions derived from petroleum crudes. The process of refining to isolate a lubricant base stock consists of a set of unit operations to remove or convert the unwanted components. They may include, for example, distillation, hydrocracking, dewaxing, and hydrogenation.
It often occurs in the course of refining a lube oil that a product is made to specification except for some deficiency resulting from contamination by a small amount of high melting wax. For example, a refined oil may be prepared that has a satisfactory pour point and cloud point, but upon storage, a wax haze develops that makes the oil commercially unacceptable.
When this haze occurs, the refiner suffers a severe economic penalty because the haze is usually discovered only after all the raw material and process costs have been expended to make the product. At this time, there is no effective and economic process to remove the small amounts of contaminating wax, present in amounts less than 2.0 weight percent. These contaminated oils generally cannot be mixed with other oils to make a commercially acceptable blend. Thus, there is no market or use for these contaminated oils other than feeding them to a catalytic cracking unit or burning them as heavy fuel oil.
In recent years, workers in the field have proposed various processes to catalytically dewax petroleum oils. For example: U.S. Pat. No. 3,755,138 (hydrodewaxing intermediate pour point solvent dewaxed lube oils for further pour point reduction); U.S. Pat. No. 4,181,598 (catalytic dewaxing, followed by hydrofinishing of solvent refined lube oils to produce low pour point, high stability lube oils); and U.S. Pat. No. 4,269,695 (catalytic hydrodewaxing of poorly dewaxed lube oils over a zeolite catalyst). In addition, U.S. Pat. No. 4,597,854 describes a multi-bed dewaxing process. But none of these patents describes a single stage, multilayered catalyst system for hydrodehazing and hydrofinishing a hydrocracked, solvent dewaxed lube oil base stock.
Because of high fluctuations in sulfur and nitrogen levels, all of these processes require relatively low liquid hourly space velocities (LHSV), less than 4 hr..sup.-1. Furthermore, if the constraint index of the zeolite catalyst is too low, a further economic penalty will result from base oil yield losses in attempting to remove traces of wax. Moreover, if dehazing is done after hydrofinishing, the oxidation stability of the lube oil may be affected. So as a practical result, the catalytic dehazing must be accomplished separately from other processes such as hydrofinishing. Accordingly, it is the principal object of this invention to accomplish both catalytic dehazing and hydrofinishing in a single process step. This is accomplished at a relatively high LHSV and high hydrogen partial pressure in order to combine both processes.
It has now been discovered that by using a multilayered catalyst system, an LHSV greater than 4 hr..sup.-1, with respect to the dehazing catalyst and hydrogen partial pressure greater than 500 psia, hydrocracked, solvent dewaxed lube oil base stocks can be catalytically dehazed and hydrofinished in a single process step. Thus, the present invention yields increased process efficiencies and reduced capital costs.